Urechis unicinctus is a species of marine spoon worm. It is widely referred to as the fat innkeeper worm or the penis fish.

Habitat
U. unicinctus, like other Urechis, lives in burrows in sand and mud. It gets the name "fat innkeeper worm" due to the fact that the tunnels it creates often contain other animals.[2]

Economic use
This spoon worm is commonly eaten raw with salt and sesame oil in Korea and in part of Japan.[3]
In Chinese cuisine the worm is stir-fried with vegetables, or dried and powdered to be used as an umami enhancer. In particular, the worm is considered an important ingredient in Shandong cuisine and is used in numerous recipes.
It is also used for fishing bait.